pi Ui

•

PRELIMINARY REPORT ON THE DEPOSIT",

OF IRON ORE AT HAMPSHIRE HILLS

INTRODUCTION

Many years ago the late Renison Bell discovered large bodies of magnetite in the valley of Emu River on the Hampshire Hills Es ta te of._ the Van Dieman' s Land Company, and also the more extensive deposits on Orown land to the east thereof recently acquired by L.J. Smith of Ulverstone. These outcrops were considered, at the time, to be the cappings of silver-lead and tin ore-bodies and quite recently even, some of them have been trenched to ascertain their value as repositories of tin ore. The occurrences near the line of contact between the granite and magnetite-bearing altered limestone rocks contain fluorspar in considerable abundance, thereby 'suggesting the latter possibility. Traces of tin have been found in the magnetite - poor section of the ore­bodies, but no important deposits have as yet been found in them. However, outside the magnetite area alluvial deposits of tin ore have been worked for many years.

At the time of the systematic investigation of the iron ore resources of Tasmania ~y th~ late Mr. W.H. Twelvetrees and the writer, the importalilce .~ these deposits was not known to the Geological Survey, and in consequence, reference is not made to them in the publication dealing with that subject issued by the Mines Department.

GEOGRAPHY

The main line of transport between Hampshire and Burnie is provided by the Emu Bay Railway Company. Hampshire Station is 1,500 feet above sea level and is nearly 20 miles from the seaport. It will thus be seen that very little tractine force is required in the conveyance of the ore between these pOints. The mines, by rail route, are distant only six miles from Hampshire, and the intervening country presents no serious obstacle to railway extension. Along the route of the proposed line, the land surface does not rise above 1,750 feet, but the crossing of Emu River is at the 1,300 feet contour. However, by extending the branch railway to Oonah Siding, one mile nearer Burnie, the grade could be reduced to 1 in 80 against the load.

Burnie is a flourishing town occupying the west and south shores of Emu Bay, one of the most important sea-pokts in the northern part of the Island. The protection afforded by a concrete breakwater extending 1,000 feet from the Western headland provides safe mooring for both small and large vessels in all weathers. At Burnie, provision is made for the. rapid handling of cargo from the snap's hold direct to railway trucks on the wharf, and vessels may enter and leave port without difficulty except during a very severe storm. Another advantage possessed by this seaport is its comparative nearness to the mainland of Australia.

The surrounding district is famous fertility of its basaltic soils and the prosperity of the inhabitants •

for the consequent

•

•

PHYSIOGRAl'HY

1i1r _ ;1, ....

The area under review may be described, briefly, as an elevated plateau traversed by numerous north­flowing streams, of which the Blythe and Emu Rivers are the more important. It constitutes a border portion of the Bischoff peneplain (1,500 to 1,800 feet above sea-level) and here, as there, is covered, in part, with a thin sheet of basal tic lava. Al thousb the old erosion surface, so conspicuous a feature of that area, is not clearly discernible here, the general accordance in levels and the absence of a definite break in the continuity of the plain through the intervening country is considered sufficient proof of their coincidence. Residual mountains of erosion, such as Valentine Peak, Mt. Mi.sery, and Companion Hill, standing a11t abruptly against the sky-line ,.b.a;ve their counterpart in the Bischoff district.

Basalt lava of Tertiary age occupies the valley and bed of Emu River hundreds of feet below outcrops of granite, pyroxenite, limestone and sandstone of early Palaeozoic age~ showing that the stream is flowing in a very old erosion channel. The contact of the eruptive rock with the older fonmations along the course of the stream is clearly exposed in m~y places. The surface, beneath the lava, in some places, is covered by rubble, much of which is enclosed in the eruptive rock.

In many parts of the ares; erosion has completely removed the basalt from the o~d peneplanated surface, exposing to view ,~dstonesr limestone and slates and the inttusive rocks amphibolite, pyroxenite, and granite, of which the bedrock is constituted. Tin ore, shed by the granite, has collected in placers or alluvial drifts in the deeper valleys, and. some of these have proved highly productive.

GEOLOGICAL RELATIONS

The rock fonmations of the district include a thick series of limestone, sandstones, grits, and conglomerates of Cambro-Ordovician age, Which, at the close of the Silurian were invaded, first, by basic rocks consisting largely of amphibolite and then by granite. Both groups of intrusive rocks are well exposed, and because of the intense mat amorphism of the sedimentary rocks especially the limestone, the great mass of the granite probably lies not far beneath the surface in the south-easter part.

Diabase, possessing all the characteristics of the intrusive rock of Upper Mesozoic age so prominent in the midland and eastern districts, abuts against the eastern edge of the granite.

Tertiary basalt occupies a large part of the plateau, and also erosion valleysof an older topography.

The basic rock is rather unique. It consist~ largely of colamnar hornblends or amphibole in lenticular masses and is highly developed. The. fresh rock consists of crystals one to six inches inlength~ To the south-east a peculiar fibrous brown variety occurs.

F I

..

• The granitic rock is remarkable for the absence

of the micas. Biotite is prominent near Hampshire Railway Station, but elsewhere its presence in appreciaDl~ proportion is unusual. Muscovite is poorly developed and occurs at widely separated points only. The rock consists essentially of orthoclase, an acid plagioclase, and quartz, and is generally of medlill.uD. grainsize. Dyke rocks associated with the granite batholithic mass include granite porphyrz and aplite. Near contacts quartz - tourmaline is prominent.

THE PROCESS OF INTRUSION AND METAMORPHISM

The intrusive igneous rocks referred to were derived from a common magma which, by differntiation in place, formed the stocks of two groups of rocks, namely: a basic group, now represented by amphibolites, and pyrOxenites, and an acidic group, represented by granites. After the completion of the se~egation of the basic from the acidic portion of the stock magma disunion was effected by the injection of the comparatively small basic portion into the overlying C .. br..Ordovician sediments. There, further dtff'tentiation resulted in the formation of mineral group. now represented by the several containing rock formations. There followed, after a short interval, the intmasion of the acidic or gran1t~ partion of the original stock magma with it. accompaaying~eralising agents. The affect of the intrusioa .1' the graDite on the sediments is not partioulafly muked, except iR. the case of the limestone which in many~.s has been completely transformed. The most important metamorphic affect of the intrusion on the limestone rocks is the development Of large bodies of crystalline lime silicate. This change is produced by the action of hot silicated waters on calcium~oarbonate. In places, at points of contact for instance, where fluorine-bearing solutions were prominent, garnet, with fluorspar, pyrophyllite, and magnetite, was developed at the expense of the original rock, and dolomite was not formed. It is evident that the variation in the products of metamorphiam is due to distinctly different solutions of different composition. The metamorphic ore-bodies are exceptional, in that they occur well within the egneouamass that caused the metamorphism. All gradations from garnet through garnet-magnetite rock to magnetite are represented.

SECTIONS 9065M, 906614, AND 9067M - L.J. SMITH, LESSEE.

AREA, SITUATION, ETC.

These sections, each of 30 acres, are situataated six miles, east of Hampshire, or Blaad., as it is officially designated, a small settlement fronting the ~u Bay Company's railway line which line which connects.Zeehan with the port of Burnie. A road leads from the siding three miles towards the mine, and the surveyed route for its extension passes through the property. The route is fairly direct, over gently undulating graSslands, as far as Holloway's sawmill, thence ·the cour'e over forest-clad granite country is rather tortuous, hut the gradient is not heavy on any section. It will thus be seen that the mine .. under present aDndi tions is easily accessible by railway, road, and track.

A

THE ORE--BODIES

The sections are almost wholly occupied by altere.d limestone rocks and by basic rocks consisting largely of amphibolite or and of pyroxenite. This body of limestone rocks is completely incased in granite, b~ at the southern end the thickness of the casing is very small compared with that on the other three sides. In them are lenticular bodies' of magnetite arranged in echelon formation with aureoles of disseminated magnetite., in garnet. Solutions emanating from tile intrusive granite. have greatly affected the limestone rock., and the .. magnetite also, especially in the ore-bodies near the granite contact. Along this line conversion into garnet is almost general, and silicification is common. Associated with the garnet is found pellucid and purple fluorspar, perfe~tly crystallized and in considerable abundance. It is striking to see a rock ' flecked with magnetite and studded with fluorspar, minerals which, as a rule , are so widely separated and which~ecur under such dissim11ar conditions. liIetaaorphism is not general . even along the line 'of contact, as instance the fresh and unaltered condition afthe small bodi}' of basic rock, completely enveloped in granite, l~ing to the west of Section 9067M. Silicification is prominent near the termini only of the body of ,limestone rock, and the larger and more important ore-bodies are noticeably uncontaminated. Garnetisation o,curs on both sides of the body and extends inwards more than one hundred feet·from the border, fOrming a garnet-magnetite fringe. The composition of the garnetised rock is as fol:lows:-

Silica Si 02 20.60 per cent

Ferric oxide Fe203 29.89 " " Ferrons oxide Fe ° 10.37 " "

Alumina Al203 17.10 " " Titania Ti 02 trace

Lime Ca ~ 21.40 " " Magnesia Mg ° 0.22 " " Manganese oxide MIlO 0.93 " " Fluorine, etc. F etc. 0.52 " ..

The high proportion of iron is accounted for by the presence of disseminated magnetite ore in the rock. The low content of magnesia is particularly striking.

QUANTITY OF MAGNETITE AVAILABLE

Within the boundaries of these sections there are nine leases of rich ore and two occur over the border. They vary greatly in size, the largest being near the centre of the limestone rock. Their thickness and extent cannot be determined with any degree of exactitude owing to the difficulty in tracing their outlines. This is due to the covering of detritus and clay soil resulting from the disintegration and decomposition of the aontaining rocks. Bedrock has been exposed at a few

•

•

points in trenohes, but these openings have been oonfined to the bodies aear the granite which were considered likely to contain eres of tin. The infoZ'lllation they reveal is of no value in so far as it conoerns the investigation of the magnetite deposits. There are then no criteria upon Which an estimate of quantity can be based.

Suffice it to state that these disconnected bodies of magnetite are distributed through the length and breadth of the three 30-acre sections, and that few are less than twenty feet in width and some are much wider.

In addition to the clean ore, largaquantities of dasseminated ores are available.

QUALITY OF THE ORE

The reason for the difficulty in arriving at an estimate of quantity is experienced again in attempting a determination of the quality of the ore. In all the ore-b,odies partial alteration of magnetite to hematite and to li~onite, especially, is apparent, but in the centre of the larger bodies the transformation is not so noticeable. It is evident that the alteration becomes less and less as "the cover increases, and that the effect of oxidising agents is greater near the sides than in the centre of the body. The more massive the ore the less the alteration, consequently the greatest change is found in the disseminated ore a .• In e~reme cases the conversion to limonite is complete, and this mineral, simulating its parent in lustre and general appearance, is often mistaken for massive magnetite. However, when these bright, limonite-coated boulders are broken, the containing basic rock is seen and their nature is plainly revealed.

No attempt was made to effect a systematic sampling of the ore to determine its value - that was impossivle - but the various grades are fairly represented in the table of analysis given hereunder. The purpose of the rough attempt at sampling was to ascertain what proportion of impurities was present in the various grades of the ore. It will be seen from the analyses that the ore, even that affected by atmospheric agents, is of high quality and contains traces only of deleterioua substances.

I

."j

* £

P.A. HOLLOWAY'S 10-ACRE LEASE

Ten chains south of section 9067M is a body of massive aagnetite enclosed within the bounds of a ten-acre lease recently secured by P.A. Holloway, of Haapshire. This ore-body is well wxpoded on a wooded hillock pro~ting thirty feet abov~ a button-rush­covered plain. Tha outcrop, oval tD shape, is about 200 ~.et long ,and 100 feet w1de, ~ probablyr.pr~8enta the upper surface of an extensive are-body. T~ exposed ore is reaarkably rach and contains insignificant amounts only of deleterious substances. Large crystals o~ msfW.e$i~e; in jhe fom of rhOmbic dodecahedra are very common in the outcropping ore-body.

As an adjunct to the-larger ore-bodies on L.J. Smith's sections, this may prove of considerable value.

EMU RIVER ORE-BODY

On the Hampshire Hilla Estate of the Van Dieman.ts Land Company anciJther body of rich magnetite iaknown. This ore-body is ~xposed on the right bank of Emu River, half a mile north of Hampshire~Ba1lway Station •. In every respeo,t t,he accurrence, isflimilar to that of the ore-bodies alre84y described,- being contained in garnetised limestone .which is almost wijolly inguphed im granite. In this case the ore isunaoubtedly a product of contact metamorRhiam.

The massive ore occurs in two lenticular bodies encased in garnet-magnetite rock. A smell opening cut into one body reveals ten feet width of high grade ore; the other has not been exposed by artificial meana.

It is quite empossible to estimate their value as sufficient exploratory work haa not been performed. Work of that character may be postponed until a commencement is made with the development of the other deposits.

THE COMMERCIAL VALUE OF THE DEPOSITS

In order to arrive at an estimate of the prospective v,alue of these ore-bodies it is necessary to ascertain:-

1. The dimensions of the several deposits.

2. The quality of the ore.

3. The cost of mining and e:x;cavation.

4. The cost of transport to the smel te:c.

Wi th regard to items Nos. 1 and 2, the necessary data can be obtained only by the performance of exploratory work: Under favourable conditions deep trenching across the ore-bodies should suffice, but tunnelling or drilling would be preferable. Having determined the outlines of the several ore-bodies, their depths may be assumed at half their lengths.

3. With one exception (Holloway's) all the ore-bodies can be worked to a depth of 100 feet by means of adits or open-cuts. The ore-body on Holloway's 10-acre

!~

A

• &

-I Q r - .

lease should be worked by the quarry method. Those on Smi th 's sections can be attacked at greates.t advantage on the east side from the V'alley of Holloway Creek. Until the necessary exploratory work has been performed it is impossibl~to express an opinion as to the best method. of operation, and it follows that an estimate of cost of production cannot be attempted.

4. On Government Railways the haulage cost per ton is one penny per mile for coal, and probably a similar charge would be made for the haulage of iron, especially in the handling of large quanti ties. The rate on the Emu Bay Company's line is not known to the writer, but as the load is with the grade it is not likely to be much higher.

Provision has to be made for the construction of six miles of branch railway from H~pshire siding to the minas.

THE ESTABLISHMENT OF THE IRON AND STEEL INDUSTRY IN TASMANIA

The~ smel ting of iron ores and the manufacture of the products into articles of commerce is a matter of great importance to Tasmania. Many years ago when conditions were not ripe an attempt was made to establish the iron smeltiDg industry at Beaconsfield, and but for the reason that the ores there contained too much chromium, sucoess mi~ht have attended the efforts of the operating Companies. (Chromium ores. are now in great demand for the manufacture of special steels). At the time the importance of the magnetite and haemattte deposits in the western and north-western districts was not known, and it is only within recent years that any sustained attempt has been made to develop them. Of late their value and extent have been carefully estimated.

By reason of its unique geographical position and its many other advantages, Burnie is the natural outlet for the products of many of the iron mines. Moreover, Burnie provides suitable sites for iron and steel smelters. At Wivenhoe, on the east side, and Cooee, on the west, good sites may be found. Wivenhoe is closer to the Blythe, Rutherford, and Dial Range haematite deposits, and is otherwise more favourable. If arrangements could be made to work these haematite deposits in conjunction with the Hampshire magnetite, a never-failing supply would be assured. Limestone, belonging to the same formation as that quarried at Melrose and~ailton, of excellent quality and in unlimited quantity, occurs near the North-Western Railway and at Hampshire. The-necessary supplies of coke for smelting would be drawn from New South Wales. If the electric smelting of these ores prove successful the coke requirement would be greatly reduced and the State Hydro-Electric Department is p.repared to supply the necessary electric power for the works of very large dimensions at satisfactory rates.

In concluding these remarks, it may be stated that Burnie possesses a safe deep-water port, a genial, mild and equable climate, a rich agricultural hinterland, a happily-settled community, and in the neighbourhood there are suitable sites for attendant industries.

21st Pebruary, 1924.

(Sgd.) A. McIntosh Reid, DIRECTOR OF MINES.

j

___ ............I

.. -....... 'l'Am,,1l 1. '.-- -- - -- _. __ t_ _______ - ___ , __ --r __ _

Registered .. Number

~ooality of - I lil:xposure.

~ature of Ore li'e:203 li'eO MnO '1'102 Or2;03 080 MgO 8102 AJ,2;03 J>2;O!L 8 •

.~91 I Seotion 90661,( Magnetite 70.38 22.50 0.64 traoe nil 0.36 0057 2.20 4.60 traoe nil I I~ema.tite Ie i . ,. .

: imonlte i ,

Four ohalns fromlMagnetlte 76.06 I

93 19.28 1.58 traoe nl1 traoe 0.10 2.00 1 .. 22 , nil trace S.W.oorner of I . ! 906&.1 I

! I

906,5U 22.63 1.56 ..

97 I seotion I Averase 72.28 0.70 trace nlil traoe 0.43 1.32 traoe nil , grade • ! 'MaB:netite -Iseleoted OH

! II ...

98 iUagnet1te 'Seotion 906]lL 95.50 1.05 1."51 traoe nil traoe 0.07 1.00 1.42 traoe Itrace •. - , I

. ~ - -.-- -I :

96 :Grab S~le froIa Iv.D.l..oo a Ore- Magnetite 79.60 14.18 0.50 trace nil 0.20 0.43 1.60 3·20 trace nU . ,

I , - body. - -_. , -- , - _. ,

'l'ABLlI 11. : ...... , ' . -- -, 1.1.1 • .,... "''1" J8. '"

- - _. --. -- . -_.- - -- --

92;~ ,Near granite 8.00 1.00 trace nU 22.55 0.43 24.08 ,.48 trace nil 2 • .39 ,

!oontaot Seot1on , ali" z1.e) 1'0 ok '1 906511 :. !!~tl:l I.

I et1te ! . - - . - --- - . ,

94- ~eG~" Oreek DolOIll1t- 6.69 - .. traoe + - 1.3.26 .3.62 se.64 10·71 - 3.75 ..

Haq,ah1re leed baa10 ... --""'-, ••• w' ~ __ ........ ""~

, rook - ._- -- - -- , - - -- .--- -'

I

95 lrrt"'Astdla Or.ek~ I ::;.u.~ 2'~46 - - traoe + 40.74 .3.98 41.36 4.02 .. 1 • .31 -I Hampshire. : r;iJ.mee to rut, 0 / .... f ~S

f .... :.0 i . l. - '-'J '.

'l :..~~ . ..,--- -- , ~ IT i-> -III 0> . CD 0 I--'CD ~

~ " --l

+-, - --nr- --- CJ ..., . - • --- -• -~ -- . -- -